Engineering hydrophobicity and high-index planes of gold nanostructures for highly selective electrochemical CO2 reduction to CO and efficient CO2 capture

In current study, we demonstrate a strategy for improving the catalytic performance of gold (Au) for carbon dioxide reduction reaction (CO2RR), specifically enhancing selectivity for CO over hydrogen evolution reaction (HER) and increasing low-level CO2 capture efficiency. This involved controlling nanostructures without any further modification. Au nanostructures having four different morphologies (i.e., degree of roughness) were fabricated via electrodeposition at varied deposition potential, resulting in different intrinsic surface hydrophobicity and exposure of high-index planes depending on the actual morphology. The roughest Au, with its combination of the most hydrophobic feature and abundant high-index planes, generated greater partial current density (jCO) and faradaic efficiency for CO (FECO) than the other Au deposits within a tested potential region: The roughest Au showed 6-fold higher FECO (95.8 %) and 327-fold higher jCO (normalized to electrode geometric surface area) at -0.75 VRHE compared to the smoothest Au. Moreover, the roughest Au exhibited excellent CO2 capture ability even at low CO2 concentration, confirmed with scanning electrochemical microscopy. These improvement at hierarchical Au for CO2RR could be ascribed to two factors. Firstly, the morphology-driven hydrophobicity provides an optimal gas-liquid-solid triple-phase interfaces, increasing the local CO2 concentration near the Au catalyst surface due to its superb CO2 capture ability. Secondly, the abundant high-index planes serve as stable active sites for CO2RR, expediting the reaction rates. Remarkably, Au with the highest hydrophobicity and enriched high-index planes, even without any chemical modification, showed excellent CO2RR catalytic performance comparable to or even better than the other previously reported Au-based catalysts.